The present invention relates to a method of growing a GaN group compound semiconductor crystal and a semiconductor base using this crystal.
A GaN group compound semiconductor crystal is usually formed on a sapphire substrate and the like by epitaxial growth via a buffer layer, because a substrate that lattice matches therewith is difficult to obtain. In this case, a lattice defect such as dislocation is introduced from a growth interface due to a lattice mismatch between an epitaxial film and a substrate, and the surface of the epitaxial film always contains dislocations of an order of about 1010 cmxe2x88x922. The dislocation in the aforementioned epitaxial film causes a current leak in a device, non-radiative center and diffusion of electrode material. Therefore, a method for reducing dislocation density has been tried.
One of such methods is a method using a selective growth as described in JP-A-10-312971. According to this method, a masking material, such as SiO2, is used to form a pattern on a substrate to allow a selective growth, and the growth is continued until this masking material is buried, thereby to effectively block dislocation with the masking material, or the propagation direction of dislocation is changed during crystal growth on the mask. As a result, the dislocation density is reduced.
However, the above-mentioned method is associated with a phenomenon in which the crystal axis of a crystal grown on the mask in the lateral direction relative to the growth plane to bury a masking material becomes inclined as the growth progresses, which phenomenon being called tilting. Since tilted crystals join on a mask, a new defect is generated there. What makes the crystal axis tilt is uncertain, but an influence of a masking material is considered to be present. A mask needs to be made after being once taken out from an epitaxial crystal growth apparatus. This could pose problems such as complicated steps, contamination of substrate, damage on a substrate surface and the like.
A high quality GaN substrate has been obtained in recent years by Halide Vapor Phase Epitaxy (HVPE) and the like. The substrate obtained thereby still has a dislocation density of 105-107 cmxe2x88x922, and to make a high quality device, a still lower dislocation density is required as well as indispensable.
It is therefore an object of the present invention to provide a semiconductor base having a high quality epitaxial film and a reduced dislocation density, without using a masking material used for conventional selective growth, such as SiO2, in epitaxial growth of a GaN group compound semiconductor crystal, and a method for growing the base. In particular, the present invention aims at providing a method for growing an epitaxial film having a higher quality by reducing the dislocation density of a GaN substrate having a relatively high quality.
The semiconductor base of the present invention characteristically comprises a semiconductor base comprising a substrate and a GaN group compound semiconductor crystal grown thereon, wherein the aforementioned semiconductor crystal comprises a layer having a greater dislocation density, and a layer adjacent thereto and having a relatively small dislocation density, and wherein an interface or a region, where an anti-surfactant material is fixed, exists between these layers.
A different semiconductor base of the present invention characteristically comprises an interface or a region, where an anti-surfactant material is fixed, directly on a substrate, and a GaN group compound semiconductor crystal grown thereon.
In these cases, the anti-surfactant material is preferably Si.
In the above-mentioned cases, moreover, a layer comprising the interface or region, where an anti-surfactant material is fixed, and the GaN group compound semiconductor crystal grown thereon may be formed in two or more multi-layers.
In the method for growing a GaN group compound semiconductor crystal of the present invention, the state of the surface of a substrate is modified with an anti-surfactant material, and a GaN group compound semiconductor material is supplied by a vapor phase growth method, thereby to form dot structures made of the GaN group compound semiconductor on the surface of the substrate, and the growth is continued until the dot structures join and make the surface flat.
According to the method for growing a GaN group compound semiconductor crystal of the present invention, a GaN group compound semiconductor film is formed on the surface of the aforementioned substrate, the state of the surface of the substrate is modified with an anti-surfactant material, a GaN group compound semiconductor material is supplied by a vapor phase growth method to form dot structures made of the GaN group compound semiconductor on the surface of the aforementioned GaN group compound semiconductor, and the growth is continued until the dot structures join and make the surface flat.